There are a number of medical conditions for which it has been found that an effective therapy involves driving current through a section of the tissue of a patient. Often, the current is driven between the electrodes of an electrode array implanted in the patient. Generally, the electrode array includes a non-conductive carrier on which typically two or more electrodes are disposed. Once the electrode array is implanted, current is driven from at least one of the electrodes, through the adjacent tissue, to at least one of the other electrodes. The current flow through the tissue influences the tissue to accomplish a desired therapeutic result. For example, an electrode array positioned adjacent the heart may flow currents to stimulate the appropriate contraction and expansion of the heart muscles.
There is an increasing interest in implanting electrode arrays adjacent neural tissue so that the resultant current flow induces a desired neurological or physical effect. In one known application, the current driven between the electrodes of an array placed on top of the dura in the vertebral column reduces the extent to which chronic pain signals are perceived by the brain. Alternatively, the array may be placed in a location where the current flow stimulates a feeling of satiation as part of an appetite suppression/weight management therapy. In another application, the current is flowed to tissue or nerves associated with the bladder or the anal sphincter to assist in control of incontinence. Electrodes may be implanted in a paralysis victim to provide muscle control and/or a sense of feeling.
The Applicants' Patent Application Nos. No. PCT/US2009/33769, FOLDABLE, IMPLANTABLE ELECTRODE ARRAY ASSEMBLY AND TOOL FOR IMPLANTING SAME, filed 11 Feb. 2009, published as WO 2009/111142 and US Pat. Pub. No. 2011/0077660, and U.S. patent application Ser. No. 12/535,717, IMPLANTABLE ELECTRODE ARRAY ASSEMBLY INCLUDING A CARRIER FOR SUPPORTING THE ELECTRODES AND CONTROL MODULES FOR REGULATING OPERATION OF THE ELECTRODES EMBEDDED IN THE CARRIER, AND METHOD OF MAKING SAME, filed 5 Aug. 2009 the contents of which are published in US Pat. Pub. No. 2011/0034977 A1, the contents of which are explicitly incorporated herein by reference, each describe electrode array that includes a carrier on which plural electrodes are arranged in a row by column matrix. An advantage of this electrode array is that it allows current to be flowed between numerous different combinations of electrodes. Depending on which electrodes are connected to associated current sources and sinks, this array can be operated so that there are two or more current flows occurring simultaneously between different sets of electrodes. Once this assembly is deployed, the practitioner can initially drive current between different combinations of electrodes. Current therefore flows through different sections of tissue. This allows the practitioner to determine between which electrodes, through which tissue, the current flow offers the greatest benefit and/or tolerable side effects. Once the optimal current flow path between the electrodes is determined, the array and its associated power supply are set to operate in this state.
In comparison to other electrode arrays with lesser numbers of electrodes, the above-described array makes it possible to flow current through more sections of tissue and to selectively focus/diffuse the current flow. In contrast to an electrode array with a smaller number of electrodes, use of the above-described array increases the likelihood that the current flow can be set to provide desired therapeutic effects, with tolerable side effects.
Still another advantage of the above-described array is that the carrier is formed from superelastic material. A superelastic material is one that, after being subjected to appreciable bending or folding, returns to its initial state. Thus, once this electrode array is formed, the assembly is then folded or rolled into a form that has a side-to-side width appreciably less than its width in the unfolded/unrolled state. A benefit of an electrode array assembly of this design is that it can be folded into a sheath. The sheath-encased electrode array assembly can then be inserted through an access cannula using a minimally invasive procedure into the patient. Once in the patient, the sheath and assembly are steered to over the tissue against which the electrodes integral with the assembly are deployed. Once the assembly is properly positioned, the sheath is opened up or removed. The opening/removal of the sheath causes the carrier to unfold. As a consequence of the carrier unfolding, the electrodes deploy over the target tissue. A more complete understanding of how the electrode array assembly can be so positioned and deployed is contained in the Applicants' Assignee's U.S. Pat. App. No. 61/166,366, DELIVERY ASSEMBLY FOR PERCUTANEOUSLY DELIVERING AN ELECTRODE ARRAY AT A TARGET LOCATION, THE ASSEMBLY CAPABLE OF STEERING THE ELECTRODE ARRAY TO THE TARGET LOCATION, filed 3 Apr. 2009, which is incorporated herein by reference the contents of which are published in WO 2010/114998 A1/US Pat. Pub. No. US 2012/0022551 A1.
Application Ser. No. 12/535,717 further describes how each electrode may be built over the control module that currents the components that source current to/sink current from the electrode. An advantage of this arrangement is that it eliminates that need to, from a central location, run a large number of conductors from the current source/sink components to the individual electrodes. Instead, a single bus, or a bus is connected to each of the control modules. Instructions transmitted over the bus inform each control module if it should, serve as a current source, be turned off, or serve as a current sink. Since there are relatively few bus conductors, these conductors can be relatively large in size. This reduces the fragility of these conductors. Further the conductors that extend from each control module to the associated electrode are relatively short in length. Also, the electrode array of this invention is further constructed so that the conductors that extend to the electrodes are oriented on axes perpendicular to the plane of the electrode array assembly. The electrode array assembly is exposed to relatively minimal stress along the axes perpendicular to these conductors. Collectively, these design features serves to reduce the stress to which these control module-to-electrode conductors are exposed and therefore, the possibility that they can break.
While the Applicants' previous inventions offer improvements over other electrode array assemblies, there are some disadvantages associated with them. Some of these disadvantages are associated with the manufacture of the array. This invention requires that openings be formed in the carriers. These openings define the void spaces in which the control modules are seated. In order to ensure that the modules do not shift position in the openings, it is necessary that they be precisely dimensioned relative to the other components of the array. There are concerns that the manufacturing processes needed to so fabricate the openings to ensure these openings are precisely sized may significantly add to the cost of fabricating the array,